Thin film dielectrics that are used in the fabrication of integrated circuits are often the mechanical weak link of the integrated circuit structure. Due to the emergence of conductors made from copper and insulators made from a fragile low dielectric constant (k) material, together with ultra thin silicon substrates for power-amp technologies, dielectric films are increasingly susceptible to damage during wire-bonding and die-mounting processes. Although the damage caused in these processes can be difficult to detect with standard inspections and electrical tests, it may later lead to field failures.
During packaging, the integrated circuit die is wire bonded to leads of a leadframe. A robotic bonding tool may be used in this operation. Such a tool generally includes a surface/wire-feed detection system that detects bond pads of the integrated circuit die, determines the height coordinates of the bond pads, and wire bonds the bond pads to the leadframe. After detecting the location of bond pads on the surface of the die, the bonding tool is lowered to a starting bond pad to determine the height coordinate of the pad and to adjust ultrasonic power without bonding. This first “learning touch” is performed without knowledge as to the accuracy of the height coordinate. As a result, the bonding tool frequently overestimates the distance to the height coordinate of the bond pad and the tip of the bonding tool, also referred to as a capillary/wedge, forcefully contacts the bond pad. This forceful contact may cause significant damage to the bond pad, the underlying dielectric film, and the die, and may later result in a field failure of the integrated circuit.
After an integrated circuit fails in the field, a failure mode analysis may be performed on the integrated circuit. Typically, in the process, bond wires are etched off the bond pads in order to determine if there was damage to the dielectric film during manufacturing which caused the field failure. However, the damage is difficult to detect through visual inspection alone, and due to the field failure of the integrated circuit as well as the etching of the bond wires, the integrated circuit is no longer useable.
Previous attempts to detect and prevent damage before releasing the integrated circuit for field use includes laborious inspection by operators using a microscope, as well as the reinforcement of bond pads with mechanical support structures. However, operator inspection is time consuming and expensive. Further, pad reinforcements can compromise device performance and fail to prevent damage caused by misaligned bonds. Finally, pad reinforcements are ineffective when used with bonds that have material irregularities, such as hillocks.
Thus, a need exists for a technique that detects damage to an integrated circuit resulting from the bonding process before the integrated circuit is released for field use.